Refrigerator



Mmh 2, 1937.

T. l. POTTER REFRIGERATOR' Filed Feb. 14, 1934 2 Sheets-Sheet 1 YINV ENToR How/451 Porri@ ATTORNEY T. I. POTTER REFRIGERATOR Filed Feb. 14, 1934 2 Sheets-Sheet 2 www l 9 ATTORNEY Patented Mu. 2, 1937 v4UNITED STATES :PATENT oFFici-z 17 Claims.

The present invention relates to automatic refrigerators and more particularly to apparatus used for domestic refrigeration. v

The invention has for an'object to provide a refrigerator having a plurality oi compartments with means for maintaining said compartments at different temperatures from each other.

A more specic object of the invention is to 'provide a refrigerator comprising a quick freezin'fgchamber for freezing ice cubes, desserts, etc.,

a storage chamber in which foods may be kept at freezing temperatures, and a cooling compartment in which a ltemperature is maintained above the freezing point but low enough to preserve foods, the latter compartment havinga relatively moist atmosphere so as to prevent d-rying out of the foods.

A refrigerator embodying a freezing compartment, a cold storage compartment and a cooling compartment is disclosed in a copending application Serial-No. 516,032, filed February 16, 1931, now Patent No. 2,056,165, issued Oct. 6, i936. an object of the present invention is to provide a diijerent construction from that shown in said copending application in which the relative art 35 with an evaporator' enclosed within the inner compartment, whereby ambient heat, will iiow. through the outer compartment and then through the inner compartment and ilnally into the evaporator, a heat impedance being inter- 40 posed between the compartments` to maintain a lower normal temperature in the inner compartment than in the outer compartment.

Another object of the invention is to provide an evaporator in the form of a partition dividing' q the inner compartment into' two chambers, one being of smaller dimensions than the other so as to maintain a lower temperature in the smaller chamber than in the larger one.

Another object of the invention is to so Droportion the parts asl to lheat impedance as well as dimensions that although the temperatures in the inner chamber are far below the freezing point, substantially no frost will forni on the outer surface of the walls thereof and hence thek outer compartment will not be robbed of moisture.

While a single evaporator may be used to cool all of the chambers it is also within the purview of my invention to provide an auxiliary non- 5 frosting evaporator in the outer cooling chamber.

v A further object of the invention is to provide a refrigerator .having a plurality of chambers, as described above, with an electrically-Operated heat pumping unit for pumping heat out of the chambers, said unit being controlled by thermosensitive means in one of the inner chambers.

Otherrobjects will appearin the following de- Y scrlption of certain embodiments of my inven- .tion and thereafter the novelty and scope of the invention will be pointed out in the claims.

In the accompanying drawings: A

' Figure Il is a view in perspective, partly broken away, showing my improved {multi-chambered refrigerator with a single evaporator for cooling all of the chambers; 1

Fig. 2 is a fragmentai view in the plane 2--2 of Fig. l;

Fig. 3 is a fragmental sectional view of another embodiment in which an auxiliary evaporator is employed, the section being taken on the line 3 3 of Fis. and

Fig. 4 is a fragmental view in section taken section taken substantially on the line M of Fig. 3. o i

The refrigerator shown in Figs. l and 2 coin- 3 prises a cabinet I0 which may have metallic walls packed with insulation Il in accordance with standard practice. A transverse metallic partii tion- I3, also lled with insulation, separates the cabinet into two main chambers, or compartments, namely, an upper compartment Il and a lower compartment I5. In the lower compartment there is a heat pumping unit I6 which may be of standard form and which, therefore, needs no special description. The upper compartment l is used for the preservation of food and, as will be described presently, encloses a pair of ln-y ner chambers. A door I 1 of usual commotion provides access to the upper compartment Il.

Since the lower compartment I5 contains the heat pumping unit it is liable to become much hotter than the outside atmosphere and consequently the partition I3 separating this chamber' from chamber Il is preferably thicker than the .side walls of the cabinet, thereby furnishing increased insulation chamber II.

In the upper portion of the chamber il is a,

casing IB. 'This casing may be carried by studs against inow of heat into I9 depending from the top wall of the cabinet. As shown in the drawings, the casing is spaced from the top and side walls of the cabinet so that there is an air space all around the casing. The walls of the casing are adapted to oifer a material resistance to the passage of heat therethrough. Preferably they are made of metal with a porcelain or enamel coating 2G applied to opposite surfaces of the metal. This coating serves primarily as a heat impedance, although at the same time it provides a surface that may readily be kept clean. The casing h3 has an opening at the forward end which may be closed by a door 2I. A snap catch 22 serves to hold the door in closed position, as shown in Fig. 2.

Within the casing I8 and near the top wall thereof, there is a partition or shelf 23 extending entirely across the casing and dividing the same into two chambers 24 and 25. The upper inner chamber 24 will hereafter be termed the freezing chamber while the lower one 22 will hereafter be known as the storage chamber. The shelf 23 is a cooling element, being preferably formed of an.upper and lower plate with an expansion coil 26 encased therebetween. This coil forms part of a refrigerant line 2l connected with the heat pumping unit IG so that refrigerant is forced through the line and through the coils and thence back to the heat pumping unit in the usual manner. An expansion valve 28 is provided at the inlet end of the coil 2B, this expansion valve being adjustable in the usual manner to control the expansion of refrigerant into the coil.

The shelf 23 is spaced from the top wall of the casing I8 sufliciently to permit of inserting trays 29 for freezing ice cubes, desserts, or any foods that require quick'freezing. The storage chamber 25 may be furnished with shelves for supporting foods, one such shelf being shown at 3D. The cooling chamber I4 may also be provided with one or more shelves 3l, as shown.

Immediately below the casing I2 there is a pan 32 to catch any drip from the walls of the casing. In order to facilitate the circulation oi air in the chamber I4 around the casing I8 a baille plate 33 depends from the rear ofthe casing to a point near the bottom of the chamber I4, this baille plate being spaced from the rear wall of the chamber I4. The heat pumping'unit is driven by an electric motor 34 and the latter is controlled by a thermostatic switch 35 with its bulb 36 located in the storage chamber 25.

In operation it will be found that an exceedingly low temperature may be maintained in the freezing chamber 24 and in the ice trays or other receptacles supported on the shelf 23 because these receptacles rest directly on the shelf and are in immediate contact with the coldest portion of the system. The storage chamber 25, on the other hand, will not be as cold as the freezing chamber because the transfer of heat to the shelf 23 is not as direct. The absorption of heat by contact of air in chamber 25 with the element 23 is comparatively slow and the only metallic contact is through the walls of the casing I8 to the edges of the shelf 23. Furthermore, these walls are only partially'insulated by their perce; lain coating and are warmed by heat from the cooling chamber I4. Also, while the volume of the storage chamber and the area. of its walls exposed to the heat of the cooling chamber, are much greater than the volume and exposed area of the freezing chamber, the heat absorbing area of the cooling element 24exposed to the storage amate? chamber is only slightly greater than that exposed to the freezing chamber (such excess of exposed area being due to a series of ribs 3l formed on the bottom of the cooling element). Hence, a materially higher temperature is maintained in the storage chamber than in the freezing chamber.

The cooling chamber I4 will be relatively much Warmer than the storage chamber because the only way in which heat can flow out of said chamber is through the Walls of the casing I, and the latter. are designed to offer such resistance to the passage of heat as to maintain a predetermined normal temperature difference between chamber ifi and chamber 25 and a greater temperature difference between chamber I and chamber 2E.'

The broad metal surfaces forming the walls of the casing act like the ns of a non-frosting coil so that practically no frost is formed on the casing, the walls of the casing being supplied with heat from the chamber I4 at such a rate .that they are very much warmer than the shelf 23. Thus an important feature of my invention lies in the utilization of the casing I8 with its cooling shelf 23 as a novel form of non-frosting refrigerating element.

It is weil established in the art of refrigeration that perishable foods should be kept at a temperature not higher than 50 degrees Fahrenheit because the curve of bacterial growth takes a sudden sharp rise above that point. On the other hand many foods are injured if subjected to a freezing temperature. Hence, I prefer to maintain a mean temperature of about 40 to 42 degrees in the cooling chamber with a normal range of a few degrees above and below said mean but with a high limit of 50 degreesvand a low limit just above the freezing point.

In the storage chamber foods are to be kept frozen and consequently the temperature must not rise above the freezing point. While it matters not to what extreme most frozen foods are chilled, this is not true of all foods, Ice creams, for instance, chilled below 12 degrees Fahrenheit become so hard that vthey cannot be cut and eaten. This is recognized by ice cream makers as a critical temperature and when ice creams are chilled below such temperature in Y the making, it is necessary to warm them before they are t to be served. Therefore, I prefer to maintain the temperature of the storage chamber with an extreme low of l2 degrees Fahrenheit and an extreme high of 32 degrees Fahrenheit. For practical purposes the normal temperature of the chamber may be maintained 'at about 18 to 20 degrees Fahrenheit.

The quick freezing chamber may be as cold as desired within the limits of practicability, but preferably its high should not exceed 12 degres Fahrenheit, or the low of the storage chamber. Above this temperature certain ice creams will not freeze quickly enough to prevent formation of a coarse crystalline structure unless the ice cream is periodically stirred. In practice, I iind that a mean temperature in the neighborhood of zero Fahrenheit is satisfactory.

It will thus be seen that I maintain in the three chambers three different ranges of temperature, each comprising roughly 20 degrees of the Fahrenheit scale, and that these ranges are determined by at least three critical temperature points, namely, 50, 32 and 12 degrees Fahrenheit.

Not only does the storage chamber serve as a place to keep and condition ice creams after they have been frozen but it provides an ideal storage place for meats which may be frozen without injury and which are actually improved by being frozen. The atmosphere in this compartment will be dry because of its low temperature and consequent low dew point, and moisture condensing on the underside of the shelf 23 will be frozen into a fine snow which may be readily scraped off, so that it is not necessary to provide any means for defrosting of the cooling element.

Foods in the dry storage chamber will 4retain their juices because such juices are quickly congealed bythe freezing temperature to which they are subjected.` If necessary, however, the foods.

may be covered to keep them from drying out over a long period of time because even ice will vaporize.

The atmosphere in the chamber I4 will retain its moisture content because its temperature is higher, and since substantially no frost is formed on the casing IB the air will not be robbed of its moisture. Thus, the foods may be kept from drying out and yet be maintained at a low enough temperature to preserve them. Such moisture as condenses on the walls of the casing may drip into the drip pan 32 but it will not be necessary to empty this pan often because it is desirable to retain as much moisture in the atmosphere oi the chamber I4 as possible, so that only occasionally will it be found that sufcient moisture has been accumulated in the drip pan to require that it be taken out and emptied. The drip pan is preferably supported on brackets 38 so that it may be slid out conveniently when desired.

In order to maintain the desired temperature diierential in the various chambers, a number of factors must be considered including certain variables which have to be balanced against one another. It is well known that there is no such thing as a perfect heat insulator and so long as the outside atmosphere is warmer than the air in the cooling chamber, heat will continue to flow permissible in the other two chambers.

through the walls of the cabinet into said cham ber at a rate per unit of exposed area depending upon the temperature head. The cooling shelf 23 must be capable of carrying oif this ambient heat faster than it flows into the chamber I4 so as to reduce the temperature of the latter to the desired normal, but the only way in which said heatmay reach the cooling shelf is through the l walls of the casing I8. These walls being enam.- eled both inside and out impede theflow of heat. Since the freezing shelf 23 contacts with the enameled walls at its edges only the thermal conductivity along this path is very limited and only part of the heat flows along the walls to the shelf. The rest of the heat passes through the walls into the chambers 24 and 25, whence it is carried by convection to the shelf 23. The heat absorbing capacity of the shelf depends upon its `surface-area and the pressure setting of the expansion valve. Hence, to reach a desired ratio of temperatures in the several chambers, the heat impedance and area of the outer walls of chamber I4, the heat impedance and area of the casing walls, and the area of and pressure drop in the shelf 23 must all be properly correlated.

The thermostatic switch may be set to fix the range of temperatures permissible in chamber 25 and hence indirectly the range of temperatures A rise of temperature in the cooling compartment I4, .is bound to be felt in the storage compartment, causing the thermostatic switch to start operation of the heat pumping unit to restore both compartments to the desired temperatures. Simfilarly an abnormal rise of heat in chamber 24, such as might result from the insertion" of warm foods therein, will reducel normal flow of heat into said chamber from chambers I4 and 25, permitting the temperature to rise in chamber 25, and this would result in operation of the thermostatic switch.

Under certain conditions it is impracticable to' rely solely upon the freezing shelf 23 to cool all the chambers.4 It will be noted that the chamber I4 is more directly affected by opening the door of the cabinet and under average conditions its heat load is more frequently augmented by the insertion of foods. I find that lt is possible to keepA the 4temperature of chamber I4 more stable by providing what is virtually an extension of the freezing shelf coil 26 in said chamber. A refrig- `the casing I8 there is an auxiliary coil 40 provided with fins 4I so as to prevent formation of frost. The coil 40 is connected in series with the main coil 26 at the low side thereof, so that a single expansion valve 28 serves for both coils. To prevent the formation of frost on the rear wall of the ycasing I because such wall is cooled on the inside by the freezing shelf and is very close to the auxiliary coil 4U, a shield 42`is provided between the coil 4d and the casing. This shield, as shown in Fig. 4, is turned inward at its upper end so that it nearly contacts with the casing. As a result air circulating around the casing I8 will not brush against the rear wall of the casing but will be diverted by the 'shield 4). Between the shield 42 and the casing I8 there is a dead air space which serves as an additional impedance to the flow of heat. Because of the auxiliary coil 4Il it is desirable to reduce the heat absorbing area of the casing I8 and this is done by providing a dead air space between the side -walls of the casing and the outer walls of the cabinet. To this end metal strips 43 are fastened to opposite sides of the casing I8 near the bottom thereof. These strips extend outwardly into contact with the side walls of the chamber I4 and then are turned inwardly as indicated at 44 to provide slideways for the drip pan 32. As a result of this arrangement air currents cannot pass up the sides of the casing I8, but instead flow upward past the door 2l of the casing and thence over the top of the casing and down at the rear of the` shield 42. The drip pan 32 extends far enough to the rear `to catch the drip from the fins 4I of the non-frosting coll in the chamber I4.

lAs in the refrigerator shown in Figs. 1 and 2 the freezing shelf abstracts heat from all of the refrigerating chambers. However, since the two side walls and the rear wallof the casing I8 are',

mostat 35 which has a bulb in the storage chamber in the casing I8. This determines the minimum temperatures in all of the chambers because heat will now from chamber Il into the casing v through the walls of the latter. However, the frequency of operation of the heat pumping unit is determined by the setting of the expansion valve 28 which controls-the pressure drop in the coils and hence the rate of heat absorption of these coils. But the expansion valve also controls the relative temperatures of the outer and inner chambers at the instant that thermostat operates to stop the heat pump. `As the valve is closed the pressure differential between the high and low sides of the refrigerant circuit is increased, producing a more rapid evaporation and hence a lower temperature, but at the same time the discharge of liquid refrigerant is reduced, and since the outer coil 40 receives only such liquid as is not vaporized in the inner coil 26, itwill be evident that the valve may be so adjusted that the thermostat will stop the heat pump before any liquid reaches the outer coil. In such case chamber lvl will be cooled only by the flow of heat through the door and top wall of the casing. After the heat pump stops heat will continue to flow slowly through the impedance walls of the casing until chamber 25 is warmed suiliciently to start the pump again. On the other hand, the more the expansion valve is opened the less vaporization will there be in the inner coil and the more in the outer coil, with the result that the temperature in chamber I4 will be correspondingly lowered before the thermostat stops the heat pump. It will be evident, therefore, that I have provided means for regulating the relative eiilciency o'r heat absorbing capacity of the two coils. The expansion valve might actually be so adjusted that the pump would have to run continuously to maintain the desired temperature differential between the chambers without ever cooling chamber 25 .enough to operate the thermostat, but, preferably, the expansion valve is set so that the outer coil will-do a large part of the work. Thus, it will more directly take care of peak loads resulting from the more frequent introduction of foods in the outer chamber.

While I have shown two embodiments of my invention it will be understood that these are to be taken as illustrative and not limitative and that I reserve the right to make such changes in form, construction and arrangement of parts as fall within the spirit and scope of the following claims. A

I claim:

1. A refrigerator comprising a cabinetformed with a thermally insulated food-cooling chamber, a refrigerating element in the upper portion of the chamber, a casing surrounding the element and spaced from the walls of the cooling chamber, said casing providing a secondary food chamber, and -a baille wall depending from the rear wall of the casing but spaced from the rear wall ofthe cooling chamber to facilitate the circulation of air about the casing.

2. A refrigerator comprising a cabinet formed with a' thermally insulated cooling chamber, a casing of heatv impedance walls supported within the cooling chamber, a horizontal partition wall of heat conducting material in the casing and dividing the latter into a freezing chamber and a storage chamber, said partition including a passage therethrough for an expanding refrigerant, the arcas and heat impeding quality of the walls of the several chambers being relatively proportioned to maintain predetermined normal refrlgerating temperatures in the several chambers without formation of frost on the outer face of the casing walls, the temperature in the storage chamber being above that in the freezing chamber and below that inthe cooling chamber, heat pumping means for circulating the refrigerantthrough said passage, and a controller constructed and arranged to arrest operation of the heat-pumping means when the temperature of said outer face falls to a predetermined minimum above the freezing point of water and to restart the heating pumping means when the temperature of said outer face rises above a predetermined maximum.

3.. A refrigerator comprising a cabinet formed with a thermally insulated cooling chamber, a casing formed with heat impedance walls within the chamber, and a heat pumping system including an evaporator in the interior of the casing. said evaporator sub-dividing the casing into a storage chamber and a smaller quick freezing chamber, the insulation of the cooling chamber and the impedance of the casing walls and the heat absorbing capacity of the heat pumping system being so proportioned and correlated that the temperature of the cooling chamber will be held within a'range of substantially 18 Fahrenheit degrees above the freezing point while the temperature of the storage chamber is held within a range of substantially 20 Fahrenheit degrees below the freezingpoint and the temperature of the quick freezing chamber is held Within a range of substantially 20 Fahrenheit degrees below the range of the storage chamber with substantially no formation of frost on the outer surface of the casing.

4. A refrigerator comprising a cabinet formed with a thermally insulated cooling chamber, a casing formed with heat impedance walls within the chamber, and a heat pumping system including a main evaporator in the interior of the casing and a non-frosting extension of the evaporator outside the casing in said chamber, said main evaporator sub-dividing the casing into a storage chamber and a smaller quick freezing chamber, the insulation of the cooling chamber and the impedance of the casing walls and the heat absorbing capacity of the heat pumping system being so proportioned and correlated that the temperature of the cooling chamber will be held within a range of substantially 18 Fahrenheit degrees above the freezing point while the temperature of the storage chamber is held within a range of substantially 20 Fahrenheit degrees below the freezing point and the temperature of the quick freezing chamber -is held within a range of substantially 20 Fahrenheit degrees below the range of the storage chamber with substantially no formation of frost on 'the outer surface of the casing.

5. A refrigerator comprising a cabinet formed with a thermally insulated cooling chamber, a casing formed with heat impedance walls within the chamber, a heat pumping system including a main evaporator in the interior of the casing and a non-frosting extension of said main evaporator outside the casing in said chamber, said main evaporator sub-dividing the casing into a storage chamber and a smaller quick freezing chamber, the insulation of the cooling chamber and the impedance of the casing walls and the heat absorbing capacity of the heat pumping system being so proportioned and correlated that the temperaturel of the cooling chamber will be held within a range of substantially 18 Fahrenheit degrees above the freezing point while the temperature of the storage chamber is held within a range of substantially 20 Fahrenheit degrees below the freezing point and the temperature of the quick freezing chamber is held within a range of substantially 20 Fahrenheit degrees below the range of the storage chamber with substantially no formation of frost on the outer surface of the' casing, and means for regulating the relative heat absorbing capacity of theimain evaporator and said extension.

6. A refrigerator comprising a cabinet ormed with a food cooling chamber, a casing within and spaced from the walls of the cooling chamber, means including an evaporator in the interior of the casing for chilling the same below the freezing point, a non-frosting extension of said evaporator outside of the casing and substantially paralleling a wall of the casing, and a shield adapted to provide a dead air-il space between said extension and the casing; the walls of the casing being formed of heat impedance material adapted to prevent the formation oi' frost on the outside of the casing. ,i

7. A refrigerator comprising a cabinet formed with a food cooling chamber, a caslngexwithin and spaced from the walls of the cooling chamber, means including an evaporator in the interior of the casing for chilling the same below the freezing point, a non-frosting extension o! the evaporator exterior to and at the rear of said casing, and a shield adapted to provide a dead air space between said extension and the casing, the walls of the casing being formed of heat impedance material adapted to prevent the formation of frost on the outside of the casing.

8. A refrigerator comprising a cabinet formed with a food cooling chamber, a casing within and spaced from the walls of the cooling chamber, means including an evaporator in the interior of the casing for chilling the same below the freezing point, a non-frosting extension of the evaporator exterior to and at the rear of said casing, and a shield adapted to provide a dead: air space ,t between said extension and the casing, the walls of the casing Abeing formed of heat impedance material adapted to prevent the formation of frost on the outside of the casing, and means for diverting convection currents from opposite sides of the casing.

9. A refrigerator comprising a cabinet formed with a food cooling chamber, a casing within and spaced from the walls of the cooling chamber,

, means including an evaporator in the interior of between the casing and the walls of the cooling i chamber atvopposite sides respectively of the `casing so as to divert convection currents from the sides of the casing.

10. A refrigerator comprising a cabinet formed with a thermally insulated main food chamber,

' a casing supported within said chamber and in spaced relation to the walls thereof and providing a secondary food chamber.. said casing having walls of h'eat impedance materiall, a refrigerating system operable to cool the chambers and comprising a chilling unit within the secondary food chamber, the heatV absorbing capacity of said unit and the heat impedance of said walls being so relatively proportioned as to cool the secondary chamber to a sharp freezing temperature while maintaining a refrigerating temperature above the freezing point of water in said main chamber without the formation of frost on the outer sur- -face rises above a predetermined maximum, said chilling unit being in the form of a Shelf dividing the secondary chamber into an upper and a lower compartment, vthe lower compartment being deeper and hence relatively warmer than the .upper compartment.

11. A refrigerator comprising a cabinet formed with a thermally insulated food chamber, a casing supported within said chamber and providing a secondary food chamber, said casing having walls of heat impedance material, a refrigerating system operable to cool the chambers and comprising a chilling unit in the casing, the heat absorbing capacity of said unit and the heat impedance of said walls being so relatively proportioned as tov cool-the secondary chamber to a sharp freezing temperature and the main chamber to a refrigerating temperature above the freezing point of water by absorption of heat through the casing without cooling the outer surface of the casing sufficiently to form frost thereon, and controlmeans constructed and arranged to arrest operationv of the refrigerating system when the temperature of said surface falls to a predetermined minimum above said freezing point and to restart the refrigerating system when the temperature of said surface rises above a predetermined maximum.

12. A refrigerator comprising a cabinet formed with a thermally insulated food chamber, a casingvsupported within said chamber and providing a secondary food chamber, said casing having walls of heat impedance material, a refrigerating system operable to cool the chambers and comprising a chilling unit in the casing, the heat absorbingv capacity of said unit and the heat impedance of said walls being so relatively proportioned as to vcool the secondary Vchamber toa sharp freezing temperature and the main cham.-v ber to a refrigerating temperature above the freezing point of water by absorption of heat through the casing without cooling the outer surface of the casing sufliciently to form frost thereon, and control means constructed and arranged to arrest operation of the refrigerating system when the temperature of said surface falls to a predetermined minimum above said freezing point and to restart the refrigerating system when the temperature of said surface rises above a predetermined maximum, said refrigerating system also including an auxiliary non-frosting chilling unit in the main chamber and outside of the casing.

13. A refrigerator comprising a cabinet formed with a thermally insulated food chamber, a casing supported within said chamber and providing a secondary food chamber, said casing having walls of heat impedance material, a refrigerating system operable to cool the chambers and comprising a chilling unit in the casing, the heat absorbing capacity of said unit and the heat impedance of said walls being so relatively proportioned as to cool the secondary chamber to a sharp freezing temperature and the main chamber to a refrigerating temperature above the freezing point of water by absorption of heat through the casing without cooling the outer surface of the casing suiiciently to form frost thereon, and control means constructed and arranged to arrest operation of the refrigerating system when the temperature of said surface falls to a predetermined minimum above said freezing point and to lrestart the refrigerating system when the temperature of said surface rises above a predetermined maximum, said refrigerating system also including an auxiliary non-frosting chilling unit in the main chamber and outside of the casing, said auxiliary unit being connected in series with the chilling unit in the casing.

14. A refrigerator comprising a cabinet formed with a thermally insulated main food chamber, a refrigerating system comprising a cooling element in said chamber, a casing enveloping said element and forming a secondary food chamber, the walls of said casing contacting with said element and constituting heat absorbing surfaces for the conduction of heat from the main food chamber into said element and being so thermally proportioned to the capacity of said element as to cool the main chamber to a refrigerating temperature above the freezing point of water without formation of frost on the outer surface of the casing while the secondary chamber is cooled by said element to a sharp freezing temperature,

and control means constructed and arranged to arrest operation of the refrigerating system when the temperature of said outer surface falls to a predetermined minimum above the freezing point and to restart the refrigerating system when the temperature of said outer surface rises above a predetermined maximum.

15. A cooling unit adapted to be installed in a thermally insulated main food chamber of a refrigerator to cool the same. said unit comprising a casing forming a secondary food chamber, and a chilling element in the casing adapted to cool both of the chambers, the walls of the casing being thermally proportioned to maintain a wide temperature differential between the interior and exterior of the casing such that the secondary chamber may be maintained at a sharp freezing temperature while the outer surface of the casing is cooled by said element to a refrigerating temperature above the freezing point of water, the walls of the casing completely enclosing the chilling unit and preventing the air of the main food chamber from contacting with a frosting surface.

16. A cooling unit adapted to be installed in a thermally insulated main food chamber of a refrigerator, said unit comprising a casing formed of heat impedance walls, an expansion coil in the casing, a finned expansion coil on the outside of the casing and connected in series with the first named coil, and an expansion valve constructed and arranged to control the admission of an expansible refrigerant to said coils, said coils and said walls being so thermally proportioned as to maintain a wide temperature differential between the interior of the casing and the exterior surface thereof so that the interior of the casing may be maintained at a sharp freezing temperature Without formation of frost on the exterior surface of the casing and on'said finned coil.

17. A cooling unit adapted to be installed in a thermally insulated main food chamber of a refrlgerator to cool the same, said unit comprising a casing forming a secondary food chamber, and a chilling element in the casing adapted to cool both of the chambers, the walls of the casing being solid and so thermally proportioned as to cool the main food chamber to a reirigerating temperature without the formation of frost on the exterior surface of the walls while the secondary chamber is maintained at a sharp freezing temperature.

THOMAS I. POTTER. 

